Peptide-based drugs are highly effective medicines with relatively short duration of action and variable therapeutic index. The present disclosure is directed to peptide-based prodrugs wherein the prodrug derivative is designed to delay onset of action and extend the half life of the drug. The delayed onset of action is advantageous in that it allows systemic distribution of the prodrug prior to its activation. Accordingly, the administration of prodrugs eliminates complications caused by peak activities upon administration and increases the therapeutic index of the parent drug.
Receptor recognition and subsequent processing of the peptide and protein agonists is the primary route of degradation of many peptide and protein-based drugs. Thus binding of the peptide drug to its receptor will result in biological stimulation, but will also initiate the subsequent deactivation of the peptide/protein induced pharmacology through the enzymatic degradation of the peptide or protein. In accordance with the present disclosure, prodrugs can be prepared to extend the peptide or protein's biological half life based on a strategy of inhibiting recognition of the prodrug by the corresponding receptor.
The prodrugs disclosed herein will ultimately be chemically converted to structures that can be recognized by the receptor, wherein the speed of this chemical conversion will determine the time of onset and duration of in vivo biological action. The molecular design disclosed in this application relies upon an intramolecular chemical reaction that is not dependent upon additional chemical additives, or enzymes. The prodrug chemistry is broadly applicable to peptide and protein based drugs where an aliphatic hydroxyl group can be accommodated in the active site and when the chemically modified derivative yields a poorly active peptide or protein. A specific example to illustrate this point would be the formation of reversible serine esters, at the active site serine, in the family of serine proteases.
Insulin is a miraculous peptide hormone. It demonstrates unparalleled ability to lower glucose in virtually all forms of diabetes. Unfortunately, its pharmacology is not glucose sensitive and as such it is capable of excessive action that can lead to life-threatening hypoglycemia. Inconsistent pharmacology is a hallmark of insulin therapy such that it is extremely difficult to normalize blood glucose without occurrence of hypoglycemia. Furthermore, native insulin is of short duration of action and requires modification to render it suitable for use in control of basal glucose. Established approaches to delay the onset of insulin action include reduction in solubility, and albumin binding. Prodrug chemistry offers the opportunity to precisely control the onset and duration of insulin action after clearance from the site of administration and equilibration in the plasma at a highly defined concentration.
The rich history of studies detailing the insulin structure-function relationship directs the amino acid locations where prodrug chemistry can be successfully employed. Insulin is a two chain heterodimer that is biosynthetically derived from a low potency single chain proinsulin precursor through enzymatic processing. Human insulin is comprised of two peptide chains (an “A chain” (SEQ ID NO: 613) and “B chain” (SEQ ID NO: 614)) bound together by disulfide bonds and having a total of 51 amino acids. The C-terminal region of the B-chain and two terminal ends of the A-chain associate in three-dimensional structure to assembly a site for high affinity binding to the insulin receptor. The selective insertion of hydroxyl groups can be accommodated without loss in potency at multiple locations within this active site region. Chemical esterification of these active site hydroxyl groups with specific dipeptides would dramatically lessen activity and serve as suitable prodrugs.
Pre-proglucagon is a 158 amino acid precursor polypeptide that is processed in different tissues to form a number of different proglucagon-derived peptides, including glucagon, glucagon-like peptide-1 (GLP-1), glucagon-like peptide-2 (GLP-2) and oxyntomodulin (OXM), that are involved in a wide variety of physiological functions, including glucose homeostasis, insulin secretion, gastric emptying, and intestinal growth, as well as the regulation of food intake. Glucagon is a 29-amino acid peptide (SEQ ID NO: 612 that corresponds to amino acids 33 through 61 of pre-proglucagon, while GLP-1 is produced as a 37-amino acid peptide that corresponds to amino acids 72 through 108 of pre-proglucagon. GLP-1(7-36) amide (SEQ ID NO: 602; the C terminus is an arginine amide) or GLP-1(7-37) acid (SEQ ID NO: 601; C terminus is a glycine) are biologically potent forms of GLP-1, that demonstrate essentially equivalent activity at the GLP-1 receptor.
Glucagon is a life-saving medicine that is used in the acute treatment of severe hypoglycemia. Oxyntomodulin has been reported to have pharmacological ability to suppress appetite and lower body weight. Clinical studies with GLP-1 like agonists have proven this family of peptides to be an effective treatment for Type II diabetes. In addition, it might be intrinsically safer than insulin therapy because of its glucose dependent action, thus eliminating the chances of hypoglycemia. Structure-activity relationship studies have shown that the N terminal histidine for each of these three peptides (glucagon, GLP-1 and oxyntomodulin) is especially important for the full action and that N-terminally extended forms severely diminish biological potency.
One disadvantage associated with the therapeutic use of these three peptides is their extremely short half-life (approximately two minutes) in plasma. Accordingly, to obtain reasonable glycemic control, native glucagon related analog peptides would need to be administered continuously for a prolonged period of time. The short half life results from the rapid degradation by Dipeptidyl Peptidase IV (DPP-IV), which cleaves between the second and third amino acids. This cleavage not only inactivates the native peptides but in the case of glucagon and GLP-1 the shortened forms are functional antagonists at their respective receptors. Accordingly, there is a need for longer-acting variants of glucagon, GLP-1, and oxyntomodulin, and related peptides, to realize the full therapeutic potential of these mechanisms of drug action.